1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device. More particularly, the present invention relates to a method of manufacturing a semiconductor device having a tungsten pattern.
2. Description of the Related Art
Since highly-integrated semiconductor device has been required to process mass information, a design rule of the semiconductor device has been rapidly reduced. A width of wirings and an interval between the wirings in the semiconductor device have been reduced so much that resistances of conductive patterns and lines used as the wirings have been remarkably augmented. To rapidly process the mass information, however, it is important to improve an operation speed of the semiconductor device by reducing the resistances of the conductive lines. Thus, forming the wirings using a conductive material having a low resistance is required.
Typically, the conductive patterns, e.g., a gate electrode or a bit line, may include polysilicon or metal silicide. However, polysilicon or metal silicide may have a relatively high resistance when reflected on development trend point view of the semiconductor device. Recently, methods for forming a conductive pattern using tungsten has been studied and developed. Tungsten may have a low resistance and a stability that is comparable to polysilicon or metal silicide.
In a conventional method for forming a semiconductor device using tungsten, a tungsten layer is formed on a substrate. A photoresist layer is formed on the tungsten layer. The photoresist layer is patterned through a photolithography process to form a photoresist pattern.
The tungsten layer is etched using the photoresist pattern as an etching mask to form a tungsten layer pattern. The photoresist pattern remaining on the tungsten layer pattern is removed by an ashing process or a stripping process. Here, a thin tungsten oxide layer is formed on the tungsten layer pattern during the etching process, the ashing process and the stripping process. Since tungsten is rapidly reacted with oxygen, tungsten may be readily oxidized. Subsequently, when the tungsten layer pattern is thermally treated under oxygen atmosphere, the tungsten oxide layer grows abnormally to create a whisker that includes W18049 on the tungsten layer pattern.
FIG. 1 is a scanning electron microscope (SEM) picture showing a surface of a tungsten layer on which a whisker is formed.
Referring to FIG. 1, a whisker 125a irregularly grows in every direction on several portions of a tungsten layer so that the tungsten layer has an uneven surface. Due to the whisker 125a, a subsequent layer may not be formed uniformly on the tungsten layer.
FIG. 2 is an SEM picture showing a cross section of a semiconductor device having a tungsten pattern.
Referring to FIG. 2, when tungsten layer pattern is formed by a photolithography process, a tungsten oxide layer is formed on the tungsten layer pattern. When a spacer including oxide or nitride is formed on a sidewall of the tungsten layer pattern, the tungsten oxide layer grows to form a whisker 225a during formation of the spacer. That is, when the tungsten layer pattern is continuously and thermally treated, the tungsten oxide layer is reacted with oxygen, and then abnormally grows to form the whisker 225a that is protrudes from the tungsten layer pattern.
The whisker may be electrically connected to a conductive pattern adjacent to the whisker to cause a short between the tungsten layer pattern and the conductive pattern. Embodiments of the invention address these and other disadvantages of the conventional art.